1. Field of the Invention
The present invention relates to a plasma processing apparatus and a plasma processing method, and more particularly to a microwave plasma processing apparatus and method utilizing an improved system for introducing microwaves.
2. Related Background Art
As plasma processing apparatuses that use microwaves as an excitation source for plasma generation, there have been known the etching apparatus, the ashing apparatus, the CVD apparatus, the doping apparatus, the cleaning apparatus, the surface modifying apparatus and the like that are used for producing semiconductor devices.
The etching of an article to be processed (hereinafter, simply referred to as xe2x80x9carticlexe2x80x9d as occasion demands) using a microwave plasma etching apparatus is carried out, for example, as follows. An etchant gas is introduced into a plasma generation chamber of the microwave plasma etching apparatus, and a microwave energy is simultaneously introduced therein to excite and decompose the etchant gas, thereby etching a surface of the article.
Furthermore, the ashing of an article using a microwave plasma ashing apparatus is carried out, for example, as follows. An ashing gas is introduced into a plasma generation chamber of the microwave plasma ashing apparatus, and a microwave energy is simultaneously introduced thereinto to excite and decompose the ashing gas, thereby ashing an organic matter such as a photoresist, etc. existing on a surface of the article.
Moreover, the film formation on an article using a microwave plasma CVD apparatus is carried out, for example, as follows. A reactive gas is introduced into a plasma generation chamber of a microwave plasma CVD apparatus, and a microwave energy is simultaneously introduced thereinto to excite and decompose the reactive gas, thereby forming a deposited film on the article.
In addition, the doping of an article using a microwave plasma doping apparatus is carried out, for example, as follows. A doping gas is introduced into a plasma generation chamber of the microwave plasma doping apparatus, and a microwave energy is simultaneously introduced therein to excite and decompose the doping gas, thereby doping a surface of the article.
With the microwave plasma processing apparatus, since microwaves of a high frequency are used as a gas excitation source, the number of electron accelerations is increased to increase the electron density, thereby efficiently ionizing and exciting gas molecules. Thus, the microwave plasma processing apparatus is advantageous in that the efficiency of ionization, excitation, and decomposition of a gas are high, so that it is possible to carry out fast, high quality processing even at a low temperature. In addition, there is a further advantage that the microwaves have a property of penetrating a dielectric, so that the plasma processing apparatus can be constituted as an electrodeless discharge type one, whereby highly clean plasma processing can be carried out.
As an example of a microwave plasma processing apparatus, there has recently been proposed an apparatus that uses an endless circular (or annular) waveguide having a plurality of linear slots radially formed in a planar H-place, as an apparatus for uniformly introducing microwaves efficiently (Japanese Patent Application Laid-Open No. 10-233295).
This microwave plasma processing apparatus is shown in FIG. 17. In the figure, reference numeral 9 designates a plasma generation chamber; W an article; 2 a support means for the article W; 11 a means for adjusting the temperature of the article; 122 a high frequency bias applying means; 7 a processing gas introducing means; 8 an evacuation means; 4 a dielectric window for separating the plasma generation chamber 9 from the atmosphere; 3 a microwave applicator with slots 23 for introducing microwaves through the dielectric window 4 into the plasma generation chamber 9; 13 an endless circular (or annular) waveguide; and 25 is an introducing port for introducing microwaves into the endless circular waveguide 13 to distribute them in the clockwise and the counterclockwise directions.
The generation of a plasma and the processing are carried out as follows. The inside of the plasma generation chamber 9 is evacuated via the evacuation means 8. Subsequently, a plasma processing gas is introduced at a predetermined flow rate into the plasma generation chamber 9 via the processing gas introducing means 7. Then, the inside of the plasma generation chamber 9 is kept at a predetermined pressure. If necessary, a bias voltage is applied to the article W with the high frequency bias applying means 122. A desired power from a microwave power source is supplied into the plasma generation chamber 9 through the endless circular waveguide 13. At this time, microwaves introduced into the endless circular waveguide 13 are distributed into two at the introducing port 25 and propagate within the waveguide 13 at a guide wavelength longer than the wavelength in the free space. The distributed microwaves interfere with each other to generate standing waves having a node or loop at every xc2xd of the guide wavelength. Microwaves introduced into the plasma generation chamber 9 through the dielectric window 4 from the slots 23 provided at such positions as to maximize the electric field, i.e., at the center of the endless circular waveguide 13 between adjoining two loops of standing waves generate a plasma in the vicinity of the slots 23. When the electron plasma frequency of the generated plasma exceeds the power source frequency (for example, when the electron plasma frequency exceeds the power source frequency of 2.45 GHz in the case where the electron density exceeds 7xc3x971010 cmxe2x88x923), the so-called cut-off in which microwaves cannot propagate through the plasma is caused. Further, when the electron density increases and the depth of penetration xcex4 defined by the following equation 1 becomes sufficiently small, microwaves propagate in a surface of the dielectric window 4.
xe2x80x83xcex4=(2/xcfx89xcexco"sgr")xc2xdxe2x80x83xe2x80x83(Equation 1)
In the equation, xcfx89 is the angular frequency of a power source, xcexco is the space permeability, and "sgr" is the plasma conductivity (for example, when the electron density is 2xc3x971012 cmxe2x88x923 or more, and when the depth of penetration is 3 mm or less, microwaves propagate as surface waves in a surface of the dielectric window 4). Surface waves introduced via adjoining slots 23 interfere with each other to generate surface standing waves whose loops are at every half wavelength of surface waves approximately defined by the following equation 2.
xcexs=xcexo/∈rxe2x88x92xc2xdxe2x80x83xe2x80x83(Equation 2)
In the equation, xcexo is the free-space microwave wavelength, and ∈r is the dielectric constant of the dielectric window. The surface standing waves leaked to the plasma generation chamber 9 accelerate electrons, thus generating a surface-wave interfered plasma (SIP). At this time, when a processing gas is introduced into the plasma generation chamber 9, the processing gas is excited by the thus generated high density plasma to process a surface of the article W placed on the support means 2.
The use of such a microwave plasma processing apparatus can generate a high density, low electron temperature plasma of a uniformity within xc2x13%, an electron density 2xc3x971012cmxe2x88x923 or more, an electron temperature 3 eV or less, and a plasma potential 15 V or less in a space with a large aperture of a diameter of 300 mm or more under the conditions of a pressure of 1.3 Pa and a microwave power of 3 kW. Thus, since the gas can fully be reacted and supplied in an active state to the article, and since article surface damage due to incident ions or charge-up can be reduced, high quality, high speed processing can be attained.
Further, under a high pressure condition of about 133 Pa such as adopted in the ashing or the like, since a plasma of a high density of 1xc3x971013 cmxe2x88x923 or more is locally generated in the vicinity of the dielectric window 4, high speed, very low damage processing can be attained.
However, when the microwave plasma processing apparatus such as shown in FIG. 17 that generates a high density, low electron temperature plasma is used to carry out processing, there are instances depending on the conditions where the balance of plasma density between the microwave introducing port 25 and a portion 26 opposite thereto is lost to cause uneven processing in the circumferential direction.
A main object of the present invention is to provide a plasma processing apparatus and a plasma processing method that can keep the balance of plasma density between the microwave introducing port and the opposite portion and can generate a high density, low electron temperature plasma, so that high quality processing can uniformly be effected at a higher rate. According to a first aspect of the present invention, there is provided a plasma processing apparatus comprising a plasma generation chamber, a support means for supporting an article, a gas introducing means for introducing a gas into the plasma generation chamber, an evacuation means for evacuating the plasma generation chamber, a microwave applicator comprising an endless circular waveguide having a plurality of microwave introducing ports and a plurality of slots, for supplying microwaves into the plasma generation chamber, and a junction means comprising an inlet for microwaves and a plurality of outlets for microwaves connected to the plurality of microwave introducing ports of the circular waveguide.
According to a second aspect of the present invention, there is provided a plasma processing method comprising the steps of introducing a gas into a plasma generation chamber and supplying microwaves into the plasma generation chamber through an endless circular waveguide, thereby plasma-processing an article, wherein the microwaves are distributed into a plurality, then introduced into a common endless circular waveguide from a plurality of introducing ports, and supplied to the plasma generation chamber via a slot formed in the common endless circular waveguide.
According to a third aspect of the present invention, there is provided a plasma processing apparatus comprising a plasma generation chamber, a support means for supporting an article, a gas introducing means for introducing a gas into the plasma generation chamber, an evacuation means for evacuating the plasma generation chamber, a microwave applicator for supplying microwaves into the plasma generation chamber, the microwave applicator comprising an endless circular waveguide having a plurality of microwave introducing ports and a plurality of slots, and a junction means having a plurality of outlets for microwaves connected to the plurality of microwave introducing ports and an inlet for microwaves, wherein microwaves are introduced such that the electric field vectors of the microwaves are in directions opposite to each other at the microwave introducing ports.
According to a fourth aspect of the present invention, there is provided a plasma processing method comprising the steps of placing an article in a plasma generation chamber, introducing a gas into the plasma generation chamber and supplying microwaves into the plasma generation chamber through an endless circular waveguide, thereby plasma-processing the article, wherein the microwaves are distributed so as to divide the incidence direction thereof into two and are supplied into the circular waveguide such that the electric field vectors of the microwaves are in directions opposite to each other at microwave introducing ports.
According to a fifth aspect of the present invention, there is provided a plasma processing apparatus comprising a plasma generation chamber, a support means for supporting an article, a gas introducing means for introducing a gas into the plasma generation chamber, an evacuation means for evacuating the plasma generation chamber, and a microwave applicator for supplying microwaves into the plasma generation chamber, the microwave applicator comprising a circular waveguide with a plurality of slots, at least two introducing ports provided in the circular waveguide, and an E-plane junction for introducing microwaves into the introducing ports such that the electric field vectors are in directions opposite to each other.
According to a sixth aspect of the present invention, there is provided a plasma processing method which uses a plasma processing apparatus comprising a plasma generation chamber, a support means for supporting an article, a gas introducing means for introducing a gas into the plasma generation chamber, an evacuation means for evacuating the plasma generation chamber, and a microwave applicator for supplying microwaves into the plasma generation chamber, the method comprising introducing microwaves distributed by use of an E-plane junction into at least two introducing ports such that the electric field vectors are in directions opposite to each other, and supplying microwaves introduced from the introducing ports into the plasma generation chamber through a slot provided in a circular waveguide, thereby processing an article.
According to a seventh aspect of the present invention, there is provided a plasma processing apparatus comprising a plasma generation chamber, a support means for supporting an article, a gas introducing means for introducing a gas into the plasma generation chamber, an evacuation means for evacuating the plasma generation chamber, and a microwave applicator for supplying microwaves into the plasma generation chamber, the microwave applicator comprising a circular waveguide with a plurality of slots, at least two introducing ports provided in the circular waveguide, and an H-plane junction for introducing microwaves into the introducing ports such that the electric field vectors are in directions equal to each other.
According to an eighth aspect of the present invention, there is provided a plasma processing method which uses a plasma processing apparatus comprising a plasma generation chamber, a support means for supporting an article, a gas introducing means for introducing a gas into the plasma generation chamber, an evacuation means for evacuating the plasma generation chamber, and a microwave applicator for supplying microwaves into the plasma generation chamber, the method comprising introducing microwaves distributed by use of an H-plane junction into at least two introducing ports such that the electric field vectors are in directions equal to each other, and supplying microwaves introduced from the introducing ports into the plasma generation chamber through a slot provided in a circular waveguide, thereby processing an article.